🔒 I might be overcomplicating this codewar task

[crystal helm]

Your task is to create a function that does four basic mathematical operations.

The function should take three arguments - operation(string/char), value1(number), value2(number).
The function should return result of numbers after applying the chosen operation.

Examples(Operator, value1, value2) --> output
('+', 4, 7) --> 11
('-', 15, 18) --> -3
('*', 5, 5) --> 25
('/', 49, 7) --> 7

[novel vine]

@crystal helm

Python help channel opened

Remember to:

• Ask your Python question, not if you can ask or if there's an expert who can help.
• Show a code sample as text (rather than a screenshot) and the error message, if you've got one.
• Explain what you expect to happen and what actually happens.

:warning: Do not pip install anything that isn't related to your question, especially if asked to over DMs.

Closes after a period of inactivity, or when you send !close.

[crystal helm]

https://www.codewars.com/kata/57356c55867b9b7a60000bd7/train/python

im given 3 parameters and i dont know how to work with them

do i just use a bunch of if statements to check for operator

import math

and then go from there?

[open sable]

You don't actually need the math library for this, but yeah, one way of going about it is a bunch of ifs.

[crystal helm]

def basic_op(operator, value1, value2):
    #your code here
    if operator == "+":
        return (value1 + value2)
    elif operator == "-":
        return (value1 - value2)
    elif operator == "*":
        return (value1 * value2)
    elif operator == "/":
        return (value1 / value2)
``` this is uglyyyyy

it passed but its soo ugly

[wooden coral]

Eh. It's simple and it gets the job done. 🙂
There are some minor things to freshen it up a little, though.

[magic valley]

You can use a dictionary as well...

[crystal helm]

def basic_op(operator, value1, value2):
    #your code here
    if operator == "+":
        return (value1 + value2)
    elif operator == "-":
        return (value1 - value2)
    elif operator == "*":
        return (value1 * value2)
    elif operator == "/":
        return (value1 / value2)
    else:
        return ValueError("Invalid operator")

print(basic_op('+', 4, 7))

how would i use a dictionary

lemme try

[wooden coral]

The brackets around the operations are not needed:

return value1 + value2
``` works just as well.

[crystal helm]

does it not help with readability?

how would i do it with a dict?

[wooden coral]

And when an if results in a return, there's no real need to use an else or elif afterward, since you can't reach the next if after the return is called.

This pattern is common:

if something:
    return blah
if something_else:
    return whatever
# and the final else can be omitted
return final_thing

[magic valley]

Key is a string, value is a function

[wooden coral]

You would need to pull in the operator module in that case. It has functions for each of the basic operations for this use case.

!d operator

🤔 Python bot, where you at? (Think it's having some issues)

[magic valley]

Poor python.

[magic valley]

I agree with this, but in case they cant, a lambda should suffice.

[wooden coral]

https://docs.python.org/3/library/operator.html#module-operator

[crystal helm]

operators = {"+": +, "-": -}

python doesnt let me do this

never worked much with dict btw

[magic valley]

Instead of + try operator.add

Or lambda x,y: x + y

[wooden coral]

Using operator stuff is a neat trick especially if you want to expand to other operations in a more complex calculator program.
This codewar kata doesn't need that complexity, but it can be achieved.
It's fun to experiment with it, at least. 🙂

[abstract orbit]

oh no, you broke it too 🤪

[crystal helm]

def basic_op(operator, value1, value2):
    operators = {"+": operator.add, "-": operator.sub, "*": operator.mul, "/": operator.div}

[magic valley]

Assuming you import operator then yes. now how do you use it?

[crystal helm]

i need to import operatror?

but the parameter is already operator

wont that have a naming confliction

[wooden coral]

import operator

ops = {
    "+": operator.add,
    "-": operator.sub,
    ...
}
...
result = ops["+"](8, 9)

As a toy example.

[wooden coral]

We can change that name, or give the import an alias.

import operator as op

Exercise for the reader. 🙂

[crystal helm]

import operator as op
def basic_op(operator, value1, value2):
    operators = {"+": op.add, "-": op.sub, "*": op.mul, "/": op.div}

[ebon summit]

Just use eval /s 😜

[wooden coral]

Some of those codewar solutions do use eval. It hurts me.

[crystal helm]

i heard eval has security issues

[magic valley]

I think you need 1 more line. what is it?

[crystal helm]

mod?

modulus?

[magic valley]

no

[crystal helm]

thats the thing, i dont know how to use what i just created to get the output i want

[magic valley]

ok, let's break it into a couple steps, how do you reference the correct function?

[crystal helm]

by calling it?

[magic valley]

not for a dictionary.

[wooden coral]

Correct. It can evaluate basically any expression from a string.
A well-crafted expression used as input could basically run any code, like deleting files on your system or stealing tokens

[magic valley]

how do you look up something in a dictionary?

[crystal helm]

.get()

[magic valley]

theres a more idiomatic way.

[crystal helm]

or similar to a list

[magic valley]

yeah.

what do you want to look up?

[crystal helm]

square bracket

[magic valley]

yeah, but what do you want to put in the square bracket?

[crystal helm]

import operator as op
def basic_op(operator, value1, value2):
    operators = {"+": op.add, "-": op.sub, "*": op.mul, "/": op.div}
    return operator[op[value1, value2]]

[magic valley]

not quite there. what thing is operator?

i should say what kind of thing is operator

[crystal helm]

i dont know

string?

[magic valley]

yes.

but do you want to get a substring for the problem?

[wooden coral]

The problem uses operator for a string such as "+".

[magic valley]

what do you want to return? What type in particular?

[wooden coral]

I know having op, operator, and operators all in the same spot is confusing here.
It might help to rename something to an unrelated name?

[magic valley]

also what kind of thing is op? Think about the types and what you can (and cannot) do with them.

[crystal helm]

i give up

my first solution was ugly but loved

def basic_op(operator, value1, value2):
    if operator=='+':
        return value1+value2
    if operator=='-':
        return value1-value2
    if operator=='/':
        return value1/value2
    if operator=='*':
        return value1*value2

this is the most viewed solution

[magic valley]

return operators[...]... what goes in the brackets?

even as more of a hint:

return operators[...](...)

[crystal helm]

its ok man i appreciate your help

i need to verify myself on upwork but its charging me

to do that

is this new?

[magic valley]

I don't know. Never used.

[crystal helm]

thank you for everyone's help! im done for today! i just wanted to solve at least 1 problem

[wooden coral]

Play around with that operators part on your own time, it can show you a bunch about using functions as objects, get you more into the internals so you can pull off more interesting tricks. 🙂

[vagrant light]

wait am I missing something why do that and not:

{ 
  "+": value1 + value2,
  "-": value1 - value2,
  "*": value1 * value2,
  "/": value1 / value2
}[operator]

extra computation, i suppose? but seems weird to care about in this example. and theres a way to get around that, too

[crystal helm]

how so karma?

[vagrant light]

instead of mapping the string to functions and then calling those functions to get the result.. just map the string to the result

def basic_op(operator, value1, value2):
  return { 
    "+": value1 + value2,
    "-": value1 - value2,
    "*": value1 * value2,
    "/": value1 / value2
  }[operator]

done

[wooden coral]

Yeah, that does the job. If it were any larger of a problem than this, the extra calculations would probably be wasteful. But it works.

[magic valley]

I like this lol. It works. I'm referring to something called function dispatch.

[vagrant light]

can avoid those too with my favorite underrated comp sci idiom

def basic_op(operator, value1, value2):
  return { 
    "+": lambda: value1 + value2,
    "-": lambda: value1 - value2,
    "*": lambda: value1 * value2,
    "/": lambda: value1 / value2
  }[operator]()

[crystal helm]

This is a beautiful piece of work

[tribal totem]

def basic_op(operator, value1, value2):
    return eval(f'{value1}{operator}{value2}')``` The eval function could be used to great effect here as well

[vagrant light]

until someone inputs ;__import__('os').system('evil command');

[abstract orbit]

and result in vulnerabilities

[crystal helm]

I heard eval is bad for security purposes but idk how

[abstract orbit]

#1424911275682430986 message is an example of that

[ornate totem]

I don't think you can have the semicolon there

[vagrant light]

you can

[ornate totem]

pretty sure semicolon must be part of a statement

[vagrant light]

!e

print(eval(f'1;print("hello!");2'))

[novel vine]

:x: Your 3.13 eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "/home/main.py", line 1, in <module>
003 |     print(eval(f'1;print("hello!");2'))
004 |           ~~~~^^^^^^^^^^^^^^^^^^^^^^^^
005 |   File "<string>", line 1
006 |     1;print("hello!");2
007 |      ^
008 | SyntaxError: invalid syntax

[vagrant light]

oh

[ornate totem]

🙂

exec takes statements

[vagrant light]

i thought it works as substitute for newline

[ornate totem]

eval only takes a single expression

[vagrant light]

well its still easy

replace ; with +

code will error but itll run the evil stuff first

[ornate totem]

indeed

[vagrant light]

!e

print(eval(f'1+print("hello!")+2'))

[novel vine]

:x: Your 3.13 eval job has completed with return code 1.

001 | hello!
002 | Traceback (most recent call last):
003 |   File "/home/main.py", line 1, in <module>
004 |     print(eval(f'1+print("hello!")+2'))
005 |           ~~~~^^^^^^^^^^^^^^^^^^^^^^^^
006 |   File "<string>", line 1, in <module>
007 | TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

[novel vine]

Python help channel closed for inactivity

This help channel has been closed. Feel free to create a new post in #1035199133436354600. To maximize your chances of getting a response, check out this guide on asking good questions.